1. Field of the Invention
This invention relates to moisture-hardening flocking adhesive systems which are solvent free and which may be used in the production of flexible elastomeric articles provided with a coating of fibers.
2. Description of the Prior Art
It is known that the surface of elastomers or other plastic surfaces can be treated with an adhesive solution followed by the application of short-staple fibers vertically to the surface in an electrical field after evaporation of the solvent. Such flocked articles have fabric-like surface with minimal friction with other materials such as glass. Profiles made from such materials may be used in applications such as sealing strips in window channels of automobiles. Other applications include flocked mats, flocked flexible shafts, flocked floor coverings, flocked rubber gloves, sticker boards for demonstration purposes, flocked clearer rollers for the spinning machine industry, textile tubes and the like.
The flocking adhesives commonly used for the production of flocked materials are commercial polyurethane adhesives based on a mixture of 2 isocyanate-terminated prepolymers. Typical formulations contain 40% by weight polyurethane prepolymer and 60% by weight of a readily volatile solvent. Dilution in the solvent gives a sufficiently low application viscosity so that the adhesive can be applied by casting, by roller or by spraying. The most common solvents used include xylene, toluene, ketone mixtures or chlorinated hydrocarbons. The solvent must be quickly volatilized so that there is no risk of explosion in the case of foamable solvents where flocking is carried out by high-voltage electrical fields in a flocking cubicle. The volatilized solvents have to be removed in accordance with environmental standards.
Typical examples of such solvent-containing flocking adhesives are disclosed in U.S. Pat. No. 4,535,121. These adhesives contain polyurethane prepolymers based on diisocyanates and polyols, aromatic dinitroso compounds as adhesion promoters, polyfunctional reaction products of isocyanates and epoxide compounds, low-boiling alkylbenzene solvents such as toluene or xylene, as well as conventional additives such as fillers, pigments and/or stabilizers. The reaction products of isocyanates and epoxide compounds are produced in the absence of water using reaction catalysts which bring about a direct reaction between the epoxide groups and the isocyanate groups. Examples of such catalysts are alkali phenolates, acetates, lactates, naphthenates and alcoholates and also alkali salts of fatty acids such as lithium stearate. These reaction products contain no epoxide groups.